Method for efficient supply of power to a microcontroller

ABSTRACT

A method and a system for supplying power to a microcontroller with a single cell. One embodiment of the present invention discloses incorporation of a power supply pump circuit with the microcontroller and their dynamic interaction. The microcontroller sends its power requirements to the power supply pump circuit and in response, the power supply pump circuit controls the operating voltage with optimal efficiency. The dynamic update of power supply pump circuit results in an efficient use of the power supply pump circuit and thus results in a reduction of the number of dry cell batteries to only a single cell. Incorporation of the microcontroller and power supply pump circuit onto a single chip reduces the pin number requirements as well as the space required on the printed circuit board.

RELATED U.S. APPLICATION

This application claims priority to the provisional patent applicationSer. No. 60/243,708, entitled “Advanced Programmable MicrocontrollerDevice,” with filing date Oct. 26, 2000, and assigned to the assignee ofthe present application.

FIELD OF INVENTION

The present invention relates to the field of power supplies forintegrated circuits. More specifically an embodiment of the presentinvention relates to a power supply pump circuits used to powermicrocontrollers.

BACKGROUND OF THE INVENTION

A controller is generally a device used to control other processes orexternal devices. A microcontroller is an electronic device, a highlyintegrated chip, which performs controlling functions. A microcontrollerincludes all or most of the parts needed for implementing a controllerbut physically, is a smaller device (e.g., and integrated circuit). Thedemands for reduction in the size of microcontrollers, due to the natureof their use, have led to the miniaturization of the electroniccomponents constituting a microcontroller. The reduction in the physicalsize of microcontrollers has caused an increase in the scope of theiruse across different fields. The spectrum of the application ofmicrocontrollers varies across different and diverse disciplines. Forexample, microcontrollers are being used in the field of medicine, forexample a pacemaker monitoring a patient's heart beats, or in the fieldof meteorology, where a microcontroller is installed in a very remotelocation to periodically record, log and report atmospheric conditions.In many instances more than one microcontroller is found in a singledevice to perform a certain function. In today's technology, almost allelectrical and electromechanical devices use microcontrollers for thepurpose of controlling or monitoring different processes.

Microcontrollers require a source of power for their operation. Mostmicrocontrollers only support 4.5 to 5 volts operations and thus requirea power source capable of supplying that amount of power. Dry cellbatteries are typically used to support a microcontroller's powerdemand. To meet such power requirements, generally 2-3 dry cells (e.g.,type AAA) power the microcontrollers. Comparing the size of electroniccomponents used in a typical microcontroller and the batteries used topower the device, the batteries are the most voluminous component in amicrocontroller. With the ever increasing demand for reduction in thesize of microcontrollers, a need exist to reduce the size of the powersupply providing power to the microcontrollers.

Effort should be made to conserve energy during all modes of operation.A typical microcontroller does not operate on a continuous basis, thedevice is generally programmed to operate based on the demand or inaccordance with a programmed schedule. Once the microcontroller performsits function it either goes to an idle mode or to a sleep mode until itis summoned to perform another function. It is during the performance ofa function, during operational mode, that a microcontroller requiresmore power to meet its operating voltage requirements. A microcontrollerhas a much lower power requirement during its idle or sleep mode thanwhen it is performing a function. For example, a microcontroller whichis installed in a remote location to measure environmental data at someregular interval need not be in its operational mode at all times. Themicrocontroller may be in its sleep mode most of the time, except whenit has to take the environmental data measurements. When measurementsare required, the microcontroller wakes up, takes the measurements, logsthe data and then goes to sleep. A microcontroller may be placed in ahalt mode, where all activities are ceased and it has no powerrequirements. The only way to wake up the device is by reset or bydevice interrupt. For example, in a laptop keyboard, where power savingis required, the microcontroller is in halt mode until it detects akeystroke. When the microcontroller detects a keystroke, it wakes up,its mode changes from sleep mode to operation mode. Therefore anefficient method is needed to supply a microcontroller with power ondemand and conserve power when the microcontroller is in sleep or idlemode.

Board space on a typical Printed Circuit Board (PCB) is limited, thusefforts should be made to optimize foot prints of the devices used andthe number of pins for inter connection. The present generation ofmicrocontrollers, requiring operating voltage of 4.5-5 volts, uses fewerbattery cells than prior generations in order to perform the same or asimilar function. To supply the operating voltage requirements with asmaller number of dry cells, a separate power supply pump circuit isused to boost the relatively lower supplied voltage value to therequired operating voltage value. A separate power supply pump circuitmeets the demand of a microcontroller as far as the operating voltage isconcerned, but such a power supply pump circuit has its owndisadvantages. A separate power supply pump circuit requires additionalspace on the printed circuit board (PCB) and additional pins forinterconnections. Space on the PCB for any device and pin connectionsare scarce commodities and efforts are always made to optimize suchrequirements. Minimizing the space requirements and reducing the numberof pins for the interconnection of devices are needs to be addressed bydesigners and manufacturers.

To efficiently conserve power, a continuous interaction between amicrocontroller and its power supply pump circuit is necessary. Such aninteraction includes the microcontroller informing the power supply pumpcircuit of its power demands and the power supply pump circuit supplyingthe required power when the power is needed. Conventional power supplypump circuits communicate with microcontroller and supply power to themicroprocessor based on the microprocessor's power demand. However, thevery process of communicating (e.g., driving input and output pins)decreases the efficiency of power conservation. Optimal operation of amicrocontroller requires efficient communication between the powersupply pump circuits and the microcontrollers.

SUMMARY OF THE INVENTION

Therefore, a need exists to minimize the space required by the batteriessupplying power to the microcontrollers. Also, a need exist to optimizethe efficiency of the communication between the microcontroller and thepower supply pump circuit in order to conserve the energy requirementsof the microcontrollers. Another need exist to reduce the space requiredby the power supply pump circuit and the microcontroller on the PCB andto minimize the number of pins required to interconnect these devices.Still another need exist to maintain the microcontroller with minimumamount of power consumption during its sleep mode. The present inventionprovides a novel solution to these requirements.

Accordingly, an embodiment of the present invention reduces the size ofa power supply pump circuit by reducing a number of battery cells usedto supply power to a device. Also, the efficiency of communicationbetween a microcontroller and the power supply pump circuit is increasedwhen both the power supply pump circuit and the microcontroller areintegrated into one circuit and are housed in a single chip.Furthermore, integrating the power supply pump circuit and themicrocontroller causes a foot print reduction on the PCB, thus satisfiesthe reduced space requirements, and reduces the number of pins used forinterconnection. This invention further optimizes the system's powerconsumption due to the dynamic interaction between the two devices(e.g., the microcontroller and the power supply pump circuit). Theexchange of information regarding the microcontroller's powerrequirements optimizes power consumption by the microcontroller andallows near zero power consumption when the microcontroller is in asleep mode.

These and other objects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodimentwhich are illustrated in the various drawing figures.

A method and a system for providing a power supply pump circuit tosupply power to a microcontroller. The power supply pump is a part ofthe microcontroller and the microcontroller dynamically interacts withthe power supply pump circuit. A battery initiates a supply of powercomprising a certain initial voltage to the power supply pump circuit.This initial voltage establishes a default operating voltage for thepower supply pump. A voltage sensor senses the default operating voltagevalue of the power supply pump circuit. The voltage sensor is aprogrammable device, and dynamically interacts with the microcontrollerto receive power requirements of the microcontroller. The voltage sensorupdates the operating voltage value in accordance with the powerrequirements of the microcontroller. A drive enable receives theoperating voltage value from the voltage sensor and maintains theoperating voltage value. The power supply pump also includes a gatedrive boost circuit. The gate drive boost circuit is configured toreceive commands from the drive enable circuit and to fluctuate theoperating voltage value according to the commands received from thedrive enable circuit. The drive enable circuit regulates the fluctuationof the operating voltage value in accordance with changes in the powerrequirements of the microcontroller. A passive precharge circuit drivesthe power supply pump before the voltage sensor and the drive enablebegin their normal operation.

A method and a system for supplying power to a microcontroller with asingle cell battery are disclosed. One embodiment of the presentinvention discloses the incorporation of a power supply pump circuitwith the microcontroller and their dynamic interaction. Themicrocontroller sends its power requirements to the power supply pumpcircuit, and in response, the power supply pump circuit controls theoperating voltage with optimal efficiency. The dynamic update of powersupply pump circuit results in an efficient use of the power supply pumpcircuit, and consequently, a reduction of the number of batteries toonly a single cell battery. Incorporation of the microcontroller andpower supply pump circuit onto a single chip reduces the number of pinsrequired for connectivity as well as the space required on the printedcircuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiment of the invention and, togetherwith the description, serve to explain the principles of the invention:

FIG. 1 is a block diagram of a typical power supply pump circuit and itsinteraction with a microcontroller.

FIG. 2 is exemplary incorporation of a power supply pump circuit and amicrocontroller.

FIG. 3 is a flowchart of the steps in a process of initiating powersupply pump operation and supplying the power requirements of amicrocontroller.

FIG. 4 is a flowchart of the steps in a process of a dynamic interactionthe power supply pump circuit and a microcontroller.

FIG. 5 is a flowchart of the steps in a process of initiating powersupply pump operation with a single cell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to preferred embodiment of theinvention, a power supply pump circuit for a microcontroller circuit,examples of which are illustrated in the accompanying drawings. Whilethe invention will be described in conjunction with the preferredembodiments, it will be understood that they are not intended to limitthe invention to these embodiments. On the contrary, the invention isintended to cover alternatives, modifications, and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims. Furthermore, in the following detaileddescription of the present invention, numerous specified details are setforth in order to provide a thorough understanding of the presentinvention. However, it will be obvious to one of ordinary skill in theart that the present invention may be practiced without these specificdetails. In other instances, well known methods, and circuits have notbeen described in detail as not to unnecessarily obscure aspects of thepresent invention.

FIG. 1 is a block diagram of system 100 which includes power supply pumpsystem 101 incorporated with microcontroller 180 on a single IntegratedCircuit (IC). As depicted in FIG. 1, system 101 includes a power supplypump circuit including a ring oscillator 110, a passive prechargecircuit 120, a drive enable 130, a gate drive boost 140, and a voltagesensor 150. Battery circuit 199 includes a single cell battery 196, aninductor 195, a capacitor 198 and a diode 190. The components 110-180are integrated “on chip” into a single integrated circuit. Thecomponents 190-198 are “off chip”.

Ring oscillator 110 generates the clock signals used by logic componentsof system 101. Ring oscillator 110 starts operating when V_(CC) 197attains some nominal initial voltage value, in this embodiment, ofapproximately 1 Volt. It is appreciated that the Ring oscillator 110 mayoperate during the sleep mode of microcontroller 180.

Passive precharge 120 causes the single cell battery 196 to operate fora short period of time, until V_(CC) 197 reaches an initial minimumvoltage for effective gate drive (e.g., approximately 1 Volt). Thisvoltage value causes interaction between all components of the powersupply pump circuit 101 and the microcontroller 180, this voltage isconsidered as the initial operating voltage. The initial operatingvoltage is achieved when passive precharge 120 shorts diode 190 causingbattery 196's current to flow through inductor 195 and chargingcapacitor 198. The current from battery 196, during a short period oftime, a transitory period, charges capacitor 198 to the level that itacts as a mini battery and can run ring oscillator 110 long enough tohave gate drive boost 140 to start its boosting operation. Passiveprecharge 120 takes itself out of the circuit as soon as V_(CC) 197 isboosted to the initial operating voltage value, in this embodiment 1Volt.

Voltage sensor 150 is a programmable device and selects the operatingvoltage for the power supply pump circuit. Voltage sensor 150 sensesV_(CC) 197 voltage after the transitory period and considers thatvoltage as the initial operating voltage. At this voltage level, voltagesensor 150 is enabled to interact with drive enable 130. It isappreciated that V_(CC) 197 voltage is common to all devices of system101 and battery circuit 199. When voltage sensor 150 senses the initialoperating voltage of 1 volt, Power On Reset Circuit (FOR), which is acircuit inside voltage sensor 150 signals the operating status of themicrocontroller 180 to voltage sensor 150. This circuit is a statedependent circuit that notifies voltage sensor 150 whether themicrocontroller 180 is waking up or is being initialized.

There is no interaction between voltage sensor circuit 150 andmicrocontroller 180 at voltages below the minimum operating voltage ofmicrocontroller 180. However, interaction between power supply pumpcircuit 150 and microcontroller 180 commences immediately after theminimum operating voltage of microcontroller 180 is reached. At thisvoltage level microcontroller 180 configures voltage sensor 150 of itsdesired parameters including its minimum operating voltage and itsfuture voltage requirements. On the other hand, POR has also notifiedvoltage sensor circuit 150 of microcontroller 180's operating status.

If microcontroller 180 is being initialized, voltage sensor 150 requestan increase in initial operating voltage from drive enable 130. Driveenable 130 commands gate drive boost 140 to start the boosting operationand to continue the boosting operation until drive enable 130 sends asubsequent command to stop the boosting operation. Drive enable 130sends a command to gate drive boost circuit 140 to stop boostingoperation when drive enable 130 is notified by voltage sensor 150 thatthe minimum operating voltage of the microcontroller 180 has beenreached. Microcontroller 180 starts its dynamic interaction with voltagesensor circuit 150 and configures voltage sensor 150 to its desiredparameters.

From this point on voltage sensor 150 notifies drive enable 130 ofmicroprocessor 180's voltage requirements and drive enable 130 commandsgate drive boost 140 to maintain the required voltage. Gate drive boost140 receives the voltage requirements from drive enable 130 andfluctuates the voltage by changing the duty cycle of transistor 160 asrequired. Gate drive boost 140 functions by turning transistor 160 on oroff. When transistor 160 is off the current flows into diode 190 andcapacitor 198. Capacitor 198 integrates current into voltage and voltagestarts to ramp up. The ramp rate is controlled by the duty cycle oftransistor 160, and is the ratio of transistor 160's off time to ontime.

For example, during a start up, Passive Precharge circuit 120 setsV_(CC) 197 equal to 1 Volt. V_(CC) 197 voltage of 1 Volt is common toall devices included in power supply system 101. When the voltagereaches the minimum operating voltage of microprocessor 180, dynamicinteraction between voltage sensor 150 and microcontroller 180 beginsand microcontroller 180 configures voltage sensor 150 with its voltagerequirements.

Gate drive boost 140 receives operating voltage requirements from driveenable 130. Gate drive boost 140 increases the operating voltage bycontrolling transistor 160. Gate drive boost functions by turningtransistor 160 on or off. When transistor 160 is off the current flowsinto diode 190 and capacitor 198. Capacitor 198 integrates current intovoltage and voltage starts to ramp up. The ramp rate is controlled bythe duty cycle of transistor 160, and is the ratio of transistor 160'soff time to on time.

In one embodiment of the present invention, the minimum operatingvoltage of microcontroller 180 is 2.7 volts. drive enable 130 commandsgate drive boost 140 to start boosting operation and ramps the voltage.When microcontroller 180 senses 2.7 volts, it initiates a dynamicinteraction with voltage sensor 150 and configures Voltage sensor 150 toits desired parameters. Voltage sensor 150 knowing the minimum operatingvoltage of microcontroller 180 and sensing the voltage value sends acommand to drive enable to stop boosting operation until commandedotherwise. From this point on, voltage sensor 150 directs the operatingvoltage according to microcontroller 180's requirements.

Gate drive boost 140 maintains the operating voltage at 2.7 level untildrive enable 130 sends another command requesting change in theoperating voltage.

FIG. 2 shows an exemplary incorporation of a power supply pump circuit101 and microcontroller 180 in a single Integrated Circuit 210. In thisembodiment of the present invention ring oscillator 110, drive enable130, gate drive boost 140, voltage sensor 150, and microcontroller 180are integrated into a single chip 210. In this embodiment of the presentinvention diode 190 is placed inside chip 210, but diode 190 could be anoff chip device or in other embodiments could be eliminated.

Incorporating power supply pump circuit 101 and microcontroller 180 intoa single chip improves communication between the two devices (e.g.,microcontroller 180 and power supply pump circuit 100). Dynamicinteraction between these devices (e.g., ring oscillator 110, driveenable 130, gate drive boost 140, voltage sensor 150) is a major factorin optimizing power consumption. Incorporating these two devices (e.g.,ring oscillator 110, drive enable 130, gate drive boost 140, voltagesensor 150) into a single integrated circuit 210 of FIG. 2 will resultin a more efficient communication. Another advantage of incorporatingpower supply pump circuit 101 and microcontroller 180 is reduction inthe footprint of single integrated circuit 210 of FIG. 2 on the printedcircuit board.

The present invention provides a single integrated circuit 210 of FIG. 2to take the place of a separate power supply pump circuit 101 andmicrocontroller 180. The present invention provides diode 190 to beintegrated inside single integrated circuit 210 of FIG. 2, outside asdepicted in FIG. 2 or could be completely left out. Leaving diode 190outside single integrated circuit 210 of FIG. 2 improves the performanceof the circuit and is also more cost effective, because a higher qualityand a less expensive diode could be used. Furthermore, a single discretepower supply pump circuit 101 has to have a voltage sensor which in anditself consume a fair amount of power. Integration of these devices intoa single integrated circuit 210 of FIG. 2 eliminates such an unnecessaryuse of power.

Another advantage of this embodiment of the present invention is thatV_(CC) 197 can provide power to devices on the printed circuit boardexternal to system 100.

FIG. 3 is a flowchart of the steps of a process 300 of initiating powersupply pump operation and dynamic response to the power requirements ofa microcontroller.

In step 310 of FIG. 3, the process 300 explains generation of an initialoperating voltage of a power supply pump circuit by using a passiveprecharge circuit for a power supply pump circuit.

In step 320 of FIG. 3, the process 300 shows boosting the initialoperating voltage to a minimum operating voltage using a voltage sensorincluded in the power supply pump circuit, the voltage sensor begins theboosting upon receiving the initial operating voltage.

In step 330 of FIG. 3, the system 300 provides the minimum operatingvoltage of the power supply to a microcontroller.

In step 340 of FIG. 3, this step of process 300 shows themicrocontroller commanding the voltage sensor to maintain the minimumoperating voltage or to increase the minimum operating voltage to ahigher operating voltage.

FIG. 4 is a flowchart of the steps of a process 400 of initiating thepower supply pump operation and a dynamic response to the powerrequirements of a microcontroller thus increasing the efficiency of thesystem.

In step 410 of FIG. 4, the power supply pump circuit and themicrocontroller are integrated into a single integrated circuit.

In step 420 of FIG. 3, the power supply pump circuit dynamicallyinteracts with the microcontroller.

In step 430 of FIG. 4, the power supply pump circuit receives a voltagerequirement of the microcontroller and efficiently provides the voltagerequirements to the microcontroller.

In step 440 of FIG. 4, the power consumption of the microcontroller isoptimized when the power supply pump circuit provides voltage to themicrocontroller when the microcontroller is in operation mode.

FIG. 5 is a flowchart of the steps of a process 500 of initiating apower supply pump operation and a dynamic response to the powerrequirements of a microcontroller, thus optimizing power consumption.

In step 510 of FIG. 5, initial operating voltage is generated byconnecting a passive precharge circuit to a battery circuit.

In step 520 of FIG. 5, the initial operation of a drive enable circuit,a voltage sensor circuit, a ring oscillator circuit, and a gate driveboost circuit is initiated at the initial operating voltage.

In step 530 of FIG. 5, the operating voltage is boosted to a minimumoperating voltage of microcontroller.

In step 540 of FIG. 5, system 500 shows monitoring the microcontroller'sminimum operating voltage using a voltage sensor device and increasingthe minimum operating voltage to a voltage level demanded by themicrocontroller.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purpose of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise form disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto and theirequivalents.

1. A method for supplying power to a microcontroller, the methodcomprising the steps of: a) generating an initial operating voltage of apower supply by using a passive precharge circuit for a power supplypump circuit; b) boosting the initial operating voltage to a minimumoperating voltage using a voltage sensor included in the power supplypump circuit, wherein the voltage sensor begins the boosting uponreceiving the initial operating voltage; c) providing the minimumoperating voltage of the power supply to a microcontroller; d) receivingcommands from the microcontroller to the voltage sensor to control thevoltage sensor to maintain the minimum operating voltage or to increaseto a higher operating voltage.
 2. The method of claim 1 furthercomprising the steps of: boosting the initial operating voltage to theminimum operating voltage using a gate drive boost circuit controlling atransistor coupled to a drive enable circuit; and controlling the driveenable circuit using the voltage sensor circuit.
 3. The method of claim2 further comprising the step of: controlling the voltage level of thepower supply by the gate drive boost circuit controlling a duty cycle ofthe transistor.
 4. The method of claim 1 further comprising the stepsof: boosting the voltage level of the power supply to a normal operatingvoltage in accordance with the commands from the microcontrollerprovided to voltage sensor; and reducing the voltage level of the powersupply to the minimum operating voltage in accordance with commands fromthe microcontroller provided to the voltage sensor.
 5. A method of claim1 wherein step a) further includes the step of generating the initialvoltage by establishing a shunt between a battery cell to a capacitorcoupled to the power supply.
 6. The method of claim 5 further comprisingthe step of deestablishing the shunt of the battery cell to thecapacitor as boosting of the initial operating voltage by the voltagesensor begins.
 7. The method of claim 1 wherein the initial operatingvoltage is 1 Volt.
 8. The method of claim 1 further comprising the stepof generating a clock signal for the voltage sensor using a ringoscillator circuit once the ring oscillator circuit receives the initialoperating voltage.
 9. The method of claim 1 wherein the power supplypump circuit and the microcontroller are integrated into a singleintegrated circuit.
 10. A method for supplying power to amicrocontroller, the method comprising the steps of: a) integrating apower supply pump circuit and the microcontroller into a singleintegrated circuit; b) allowing the power supply pump circuit todynamically interact with the microcontroller; c) receiving by the powersupply pump circuit a power supply requirement of the microcontrollerand efficiently providing the power supply in accordance with thevoltage requirement; and d) optimizing power consumption of themicrocontroller by providing the power supply to the microcontrollerwhen the microcontroller is in an operation mode.
 11. The method ofclaim 10 wherein integrating the power supply pump circuit and themicrocontroller into a single integrated circuit eliminates a need todrive a separate input pin and a separate output pin, resulting in anincreased efficiency of a communication between the power supply pumpcircuit and the microcontroller.
 12. The method of claim 10 wherein themicrocontroller dynamically interacts with the power supply pump circuitand configures the power supply pump circuit with the power requirement,the power supply pump circuit provides power to the microcontroller inaccordance with the power requirements.
 13. The method of claim 10wherein integrating the power supply pump circuit and themicrocontroller results in using a single integrated circuit, reducingfootprint on a printed circuit board.
 14. The method of claim 10 whereinintegrating the power supply pump circuit and the microcontroller into asingle integrated circuit reduces pin connection requirements to onepin.
 15. The method of claim 10 wherein integrating the power supplypump circuit and the microcontroller into a single integrated circuiteliminates the requirements of a separate monitoring device for anindependent power supply pump circuit.
 16. A method for supplying powerto a microcontroller, the method comprising the steps of: a) generatingan initial operating voltage by connecting a passive precharge circuitto a battery circuit; b) initializing operation of a drive enablecircuit, a voltage sensor circuit, a ring oscillator circuit, and a gatedrive boost circuit at the initial operating voltage; c) boosting theinitial operating voltage to a minimum operating voltage of themicrocontroller; and d) monitoring the microcontroller's minimumoperating voltage using the voltage sensor circuit and increasing theminimum operating voltage to a voltage level demanded by themicrocontroller.
 17. The method of claim 16 wherein the battery circuitincludes a single dry cell, an inductor, a diode and a capacitor. 18.The method of claim 16 wherein the battery circuit requires only one drycell battery.
 19. The method of claim 16 wherein the battery circuitincludes a single dry cell, an inductor, and a capacitor.
 20. The methodof claim 16 wherein the battery circuit may supply power to otherdevices on a printed circuit board.
 21. The method of claim 16 whereinthe battery circuit is an off chip circuit.
 22. The method of claim 16wherein the passive precharge circuit allows the power supply pumpcircuit to operate before the voltage sensor and the drive enablecircuit begin their normal operation.